The present invention relates to an automatic loader in a substrate processing apparatus such as a sputtering apparatus for sequentially receiving substrates or wafers from a cassette and processing the substrates, wherein the loader automatically loads and unloads each substrate with respect to the substrate processing apparatus.
Loading/unloading of wafers with respect to a sputtering apparatus in the semiconductor IC fabrication process is performed in accordance with a cassette-to-cassette system. According to this system, a cassette loaded with wafers is inserted in a vacuum apparatus, wafers are removed from the cassette and subjected to wafer processing such as film deposition in the vacuum apparatus, and the wafers are recovered in the cassette.
In such an automatic loader, however, an operator must insert the cassette in the vacuum apparatus and remove it after film deposition is completed. High-speed automation in the IC fabrication process cannot therefore be achieved.
In several other conventional systems, a cassette is placed in an outer atmosphere outside a vacuum chamber and is fed into the vacuum atmosphere. U.S. Pat. No. 4405435 describes a "continuous sputtering apparatus" having an external housing means for holding cassettes near different inlet and outlet ports. In this structure, a cassette for supplying unprocessed wafers is different from a cassette for receiving processed wafers. Only a single cassette can be placed at each of the inlet and outlet ports. Japanese Patent Disclosure No. 57-63677 describes a "continuous vacuum processing apparatus" having a means for changing two auxiliary wafer holders placed near inlet and outlet ports. The main feature of the invention lies in that the auxiliary wafer holders are standard accessories. A cassette used in another fabrication process is not used as an auxiliary wafer holder. This conventional technique provides an automatic loader having at least two cassettes exposed in the outer atmosphere. However, in such an automatic loader, a cassette for holding unprocessed wafers is different from a cassette for holding processed wafers, and the two cassettes are separated from each other. In order to automate the semiconductor IC fabrication process in a clean room, demand has arisen for an automatic loader for unloading processed wafers into the same cassette from which unprocessed wafers were supplied, without a need to move the cassette.